1. Field of the invention
The invention concerns design of vessel hulls. More specifically, the invention concerns the shape of ships' fore body forms.
2. Related Art
When a ship is moving in—and relative to—water, it is subjected to various forms of resistance by the water. This is discussed by O. M. Faltinsen, Sea Loads on Ships and Offshore Structures, Cambridge, 1990.
The resistance components in various conditions can be summarized as follows:    calm water resistance, when there are no waves,    added resistance in short (small) waves, and    added resistance in long waves (higher seastates).
Most important is the total resistance, which is a combination of calm water resistance and the added component due to the waves.
Thus, the added resistance due to waves is usually divided into two components:    a) added resistance due to reflection of waves in the bow region of the ship, and    b) added resistance due to ship motions.
The wave length regions where the different components dominate are shown in FIG. 1, illustrating typical wave length (λ) dependence of added resistance in waves for a ship of length “L”. The figure shows the two components of resistance increase, as well as the total resistance increase.
Typically, added resistance due to bow wave reflection dominate when the wave length λ is less than half the ship length (λ/L<0.5), while the added resistance due to ship motions are dominant when the ship motions become large. This is typically in the region 0.7<λ/L<1.5, where the wave length is close to the length of the ship.
When a ship goes in a seaway, the waves induce motions in six degrees of freedom on the hull. From a resistance point of view, the heave and pitch motions are the most important, which again are strongly coupled. When the hull heaves and pitches it generates its own wave system, which carries energy away in much the same way as the still water wave pattern and thereby creating a resistance force.
The added resistance in small waves is due to bow wave reflection (cf. FIG. 1), which again is very dependent on bow shape geometry and forward speed. The ship has very little, or none, motions in these waves as the ship motions are dominated by the inertia forces in this frequency range.
In order to design an effective bow to minimize the calm water resistance and the added resistance in waves, knowledge of the most probable sea conditions, wave heading, speed and operational profile is required.